This invention relates to an improved process for converting coal or similar solid carbonaceous materials. More particularly, this invention relates to an improved process for liquefying coal and similar solid carbonaceous materials.
As is well known, coal has long been used as a fuel in many areas. For several reasons, however, such as handling problems, waste disposal problems, pollution problems and the like, coal has not been a particularly desirable fuel from the ultimate consumers point of view. Moreover, coal cannot be used directly in areas where a liquid or gaseous fuel is required. As a result, oil and gas have enjoyed a dominate position from the standpoint of fuel sources, throughout the world.
As is also well known, proven petroleum and gas reserves are shrinking throughout the world and the need for alternate sources of energy is becoming more and more apparent. One such alternate source is, of course, coal since coal is an abundant fossil fuel in many countries throughout the world. Before coal will be widely accepted as a fuel, however, it is believed necessary to convert the same to a form which will not suffer from the several disadvantages alluded to previously and which will permit use in those areas where liquid or gaseous fuels are normally required. To this end, several processes wherein coal is either liquefied and/or gasified have been proposed heretofore. Of these, the processes wherein coal is liquefied appear to be more desirable since a broader range or products is produced and these products are more readily transported and stored.
Of these several liquefaction processes which have been heretofore proposed, those processes wherein coal is liquefied in the presence of a solvent or diluent, particularly a hydrogen donor solvent or diluent, and a hydrogen containing gas appear to offer the greater advantages. In these processes, liquefaction is accomplished at elevated temperatures and pressures and hydrocarbon gases are invariably produced as by-products. For the most part, however, these processes result in relatively high yields of higher boiling point liquids, i.e., products boiling in the fuel oil and the vacuum gas-oil ranges. The bulk of the products obtained from these processes are, then, at best substitutes for coal in applications where coal could be used directly. Moreover, in those processes wherein a portion of the liquid product is separately hydrotreated and used as solvent, a significant amount of saturated materials may be contained therein and these, in turn, can cause operating problems such as coking in preheat furnaces. The need, therefore, for an improved liquefaction process which will permit increased yields of lighter boiling liquid products and permit operation with a solvent containing a reduced amount of saturated, naphthenic materials and higher amounts of aromatic and hydroaromatic materials is believed to be readily apparent.